Rebel sources told the BBC that they had broken into the prison, and had made progress in their fight against government forces.

Clashes were reported throughout the day.

The rebels have not stated what the purpose of the assault was, but the jail is reported to be holding some 250 inmates linked to the anti-government uprising.

In other developments:

Web-monitoring groups say the internet had gone down across Syria for the second time in two weeks

The UN General Assembly approves a non-binding resolution calling for a political transition in Syria

'Eat your hearts'

The rebel Free Syrian Army (FSA) has vowed to punish criminals after a video appeared online apparently showing one of its commander cutting out the heart of a soldier.

"Any act contrary to the values that the Syrian people have paid their blood and lost their homes to will not be tolerated, the abuser will be punished severely even if they are associated with the Free Syrian Army," the FSA said, according to AFP news agency.

"The perpetrator will be brought to justice."

The FSA said its field commanders would investigate the video, which shows well-known rebel commander Abu Sakkar standing over the soldier's corpse as he says: "I swear to God we will eat your hearts and your livers, you soldiers of Bashar the dog."

US-based Human Rights Watch said his actions were a war crime.

The UN says nearly 80,000 people have been killed since the uprising against President Assad began in March 2011, and millions have fled their homes.

BBC World Service's Newshour will broadcast a two-hour special edition about Aleppo at 19:00 GMT on 15 May.